Investigation of the molecular mechanisms whereby acetylcholine and other cholinomimetics cause their effects at the neuromuscular junction is the subject of this application. Measurements of agonist induced changes in membrane conductance, using the voltage clamp technique, from single visualized endplates in garter snakes twitch and slow muscle fibers will be kinetically modelled. Both spontaneously occuring miniature endplate events and conductance fluctuations will be used. Dose response experiments are planned in which the ionic activity of the cholinergic agonist will be monitored directly with an ion-selective microelectrode. In addition, desensitization studies and experiments to characterize the rate limiting step in the chemically mediated membrane conductance change will be undertaken.